Jimi Hendrix was a brilliant guitarist and live performer but his real legacy may be as rock’s great bequeather. So prolific was Hendrix in the studio that four decades after the guitarist’s brief recording career and untimely death, his estate continues to release previously unheard material. The latest is “Valleys of Neptune,” an album containing 12 songs recorded during the period between the dissolution of the Jimi Hendrix Experience and Hendrix’ formation of Band of Gypsys.

Released by Sony Legacy in conjunction with Experience Hendrix, the company that oversees the guitarist’s estate, “Valleys” is being touted as a “never commercially available” collection of songs. Such claims typically carry the whiff of a cash-in: half-finished demos or re-hashed material put together to appeal to super fans and completists. A quick peak at the track list does not ease suspicions. Included are several alternate takes of well-known Hendrix songs (“Stone Free,” “Fire,” “Red House”) as well as two covers (“Sunshine of Your Love” and “Bleeding Heart”).

John McDermott, the catalog director for the estate and album co-producer, acknowledged “Valleys” isn’t for the casual listener. “If you’re a beginning fan and you don’t have ‘Electric Ladyland,’ go there,” he said, referring to Hendrix’ landmark double album. Still, he said, the record captures an interesting point in Hendrix’ musical evolution and shows a “growing sophistication” and move away from straight rock towards “more dense tracks that allow him to combine some funk and R&B.”

The record is noteworthy for other reasons. It contains the first tracks Hendrix recorded with bassist Billy Cox, an old Army buddy he called to replace Noel Redding, who had fallen out with Hendrix for, among other reasons, his obsessive tinkering in the studio. “Valleys” also includes early versions of songs that would later be re-worked and show up on other albums, in particular “Lullabye for the Summer,” which Hendrix transformed into “Ezy Rider,” a minor classic released after the guitarist’s death on “The Cry of Love” (See video below.)

Asked if there are future releases planned, McDermott not surprisingly answered in the affirmative. “He built his own studio — that was a big priority,” McDermott said of Hendrix, referring to Electric Lady Studios. “Jimi could go in and record and use the studio as a creative tool. That’s where the volume of material comes from. It wasn’t like someone from the label was saying, ‘Okay, Jimi, the Tremeloes are here at 11. You’ll have to get out.’”

*An earlier version of this piece referred incorrectly to the name of a Jimi Hendrix album. it is “The Cry of Love,” not “The Cry of Freedom.”